1. Field of the Invention
The present invention relates to carbamoyl-phosphate synthetase of coryneform bacteria, and a gene therefor. The gene can be utilized for production of carbamoyl-phosphate synthetase and subunits thereof, breeding of L-arginine-producing bacteria and nucleic acid-producing bacteria and so forth.
2. Description of the Related Art
Carbamoyl-phosphate synthetase is an enzyme that catalyzes the reactions producing carbamoyl phosphate from carbonic acid, ATP and glutamine. Carbamoyl phosphate produced by these reactions serves as a source of carbamoyl group required for the reaction producing citrulline from ornithine in the L-arginine biosynthetic pathway. Furthermore, carbamoyl aspartate produced from aspartic acid and carbamoyl phosphate is one of the intermediates of the pyrimidine biosynthesis system including uridine 5′-monophosphate.
Carbamoyl-phosphate synthetase consists of two subunits, and it has been known for bacteria belonging to the genus Escherichia or Bacillus that those subunits are encoded by carA and carB genes.
However, as for coryneform bacteria, there have been no findings about the carbamoyl-phosphate synthetase activity and enzymes therefor, and any genes therefor have not been elucidated.
Incidentally, it has been reported that when a transformant of Escherichia coli to which introduced a plasmid harboring the genes carA, carB, argI and arg box was cultured in the medium added with glutamine which is substrate of carbamoyl-phosphate synthetase, the concentration of intracellular L-arginine was the same as that of a control strain to which only the vector was introduced. However, when the transformant was cultured in a medium added with glutamine accompanied with ornithine which is a substrate of ArgI together with carbamoyl phosphate, the concentration of intracellular L-arginine was higher than that of the control strain (Malamy M. et al., Applied Environmental Microbiology, 63(1), 33 (1997)). From these result, it was suggested that the rate-determining step of synthesis of L-arginine is supply of ornithine.
There was thought to be a possibility that the rate-determining step of supply of ornithine is N-acetylglutamine synthetase (ArgA). ArgA suffers feedback inhibition by the final product, L-arginine, in the biosynthesis pathway of Escherichia coli. 
As for the strain in which argA gene coding for feedback inhibition-desensitized ArgA was amplified by plasmid, the concentration of intracellular L-arginine was increased even in a medium added with only glutamine as well as in a medium added with both glutamine and ornithine. However, farther increase of concentration of intracellular L-arginine was not observed in the case that the strain was cultured with addition of glutamine, or glutamine and ornithin, also in the case that the both of carA and carB genes were further amplified in the strain (Malamy M. et al., Applied Environmental Microbiology, 64(5), 1805 (1998)).
On the other hand, any attempts have not been reported to enhance L-arginine productibity of microorganisms by utilizing a gene coding for carbamoyl-phosphate synthetase derived from coryneform bacterium.